1. Field of the Invention
The invention relates to internal combustion engines for aircraft. More particularly, the invention relates to an internal combustion engine that uses hydrazine as a monopropellant in a turboprop engine for a high altitude aircraft.
2. Background Art
For aircraft that operate at very high altitudes, the choice of a propulsion system generally does not include internal combustion engines, including turbine engines. As used within this specification, very high altitudes means altitudes up to and including about 110,000 feet. At these altitudes, air pressure is so low (about 0.6 inHg, an average, compared to about 29.92 inHg. at about sea-level, on average) that conventional gas turbines, fueled by hydrocarbons, are impractical for at least two reasons. First, low air pressure slows the combustion reactions in the engines combustion chamber to the extent that combustion cannot be stabilized in a practical configuration. Secondly, the low air pressure lowers the Reynolds number of the air flow in the engine's compressor and turbine, exacerbating the effects of viscous flows and lowering the efficiency of the compressor and turbine. In gas turbines, the useful power is the difference of the turbine and compressor powers, and henceforth depends critically on the efficiency of these two components. The effects of low air pressure and low Reynolds numbers are such as to limit conventional gas turbines to flight altitudes of approximately 65,000 feet or less.
However, as those of ordinary skill in the art can appreciate, expanding the regime in which gas turbine engines can operate can be extremely beneficial. Gas turbine engines have a good power-to-weight ratios, and exhibit high efficiency at lower subsonic airspeeds (300 knots plus).
Thus, a need exists to develop a gas turbine engine that can operate at very high attitudes.